docs: def at(self, timestamp=None, **kwargs):
          """
          at(timestamp) -> SubRipFile clone
  
          timestamp argument should be coercible to SubRipFile object.
  
          A specialization of slice. Return all subtiles visible at the
          timestamp mark.
  
          Example:
              >>> subs.at((0, 0, 20, 0)).shift(seconds=2)
              >>> subs.at(seconds=20).shift(seconds=2)
          """
          time = timestamp or kwargs
          return self.slice(starts_before=time, ends_after=time)